Electrolytic production of thin



y M E. ,ww M .Nm. v wfiw Rw w, 4 5% v wztfim WEEEHQ Dec. 30, 1947. c. DAVIDOFF ELECTROLYTIC PRODUCTION OF THIN METAL FOIL w Filed April 1, 1943 Z9555 Eiam E93? E56 Patented Dec. 30, 1947 E'HCE ELECTROLYTIG PRODUCTION F THIN METAL FOIL Charles David fis New York, N. Y., assignor to M. Swift &, Sons, 1110., a corporation of Connecticut Application April 1, 1943, Serial No. 481. L09

less steel, which may be of any suitable length, although a stainless steel drum would serve the same purpose. I have found that an 1 8% (Zr-8% Ni stainless steel depositing base, which has, been film therefrom. It is an object of the invention work-hardened and tempered, has a greater life to provide an improved method for producing an than an annealed ordead soft base. improved metal foil. A more specific object is I have further found that the use of other to provide a continuous and uninterrupted process depositing bases is attended by various disadentailing the deposit of the foil on an endless vantages, including the frequent and expensive metal depositing base, the formation of a rein- 10 repreparation of the surface of any relatively forcing film on th foil, the mechanical stripping soft, metal depositing base, such as copper Qr of the foil from the base, the removal of the nickel, as by forming and maintainin thereon reinforcing film from the foil, the backing of a film of an oxide or a sulph e. the foil, and its assembly in roll form for com- I furthermore have found that by the use of mercial use. The metal foil so produced may be stainless steel as a depositing base it is not Only of gold, silver, copper, nickel, or alloys of such possible, to secure a continuous deposit which metal, or substantially any metal or alloy which is readily removable me a y wit out marmay be deposited from a plating bath. ring the depositing base and without interrupt.-

With the above and other objects and advaning the continuity of the operation, but it also is tageous features in view, the invention consists possible, by changing the degree and type of of a novel method more fully disclosed in the polish of the stainless steel depositing base to detailed description following and in the accomobtain a desired thickness of the deposited metal. panying drawings and more specifically defined The following table gives the film thicknesses in the claims appended hereto. attainable, with different finishes:

. 16 Kar Gold. Description of Finish 24 Karat Gold l(gold- Silver Al- Copper Brass Approx. 0.000014- Approx. 0.000005".

Approx. 0.000001 Approx. 0.0001-.- Approx. 0.000038.

Approx. 0.000025".

AItJDIOX. 0.000005 Approx. 0.090005 Approx. 0.000038.

to 0.00001 0 0.00001. Approx. 0.000001" Approx. 0.000001 Approx. 0.000015.

to. 0.000005". to 0.000005.

In the drawings Fig. l is a schematic plan of the apparatus for preparing the metal plating base, for plating the foil thereon, for applying a reinforcing pulloff coating to the foil and for mechanically stripping the reinforced foil from the base.

Fig. 2 is a preferred apparatus for adding an embossing foil support.

Fig. 3 is a perspective view of the embossing strip before the null-on coating has been removed, and

Fig. l is a perspective view of the completed embossing strip.

By my method have produced a continuous strip of commercial metal foil of any desired length and having any desired width and a thickness within the ranges hereinafter shown. In making such foil I have employed a depositing base in the form of an endless band of stain Up to new stainless steel has not been satisfactorily used so as to permit of its utilization in com mercial practice. This has been due to the fact that frequently the foil adheres so firmly to the base as to malge mechanical stripping therefrom impossible.

I have also found in the manufacture of extremely thin foil of the type with which we are here concerned that another factor frequently makes impossible the continuous deposit of foil upon an endless band or cylinder. This difficulty is occasioned by the fact that foil of this nature does not in itself possess suificient tensile strength to permit of mechanical stripping without rupture unless it is reinforced by a pull-off film, which is applied to the foil in liquid state. Extremely thin foil frequently is porous and While this porosity is ordinarily invisible to the naked eye and does not affect the commercial value of the fi ished prodnot for usual purposes, I have discovered that its pores are penetrated by the liquid pull-off film, which hardens upon and adheres to the depositing base in such way that subsequent electrodeposition thereon is in the form of a powdery mass rather than the desired continuous film.

This penetrating deposit on the base must be removed. I prefer to remove it by the employment of the apparatus hereinafter disclosed although it also may be removed by a suitable washing in a proper solvent. I also have discovered that the depositing base itself may be so treated as uni formly and continuously to allow the foil to be stripped therefrom.

In the preferred practice of my process, I first cause the depositing base to pass under a series of polishing heads which are covered with a textile material, the preferred material being woven of a mixture of soft wool and silk threads which are preferably wetted with a solution of finely suspended alundum so fine that it will not affect the polish of the depositing base but will aid the polishing heads in removing the minute particles of pull-off film which still adhere thereto after the stripping operation. In lieu of the polishing heads as described above, I may use open cotton buffs wetted as above,'and rotating against the surface of the depositing base. Thereafter I cause the depositing base to be electrolytically treated, using the depositing base as an anode in an alkaline electrolytic bath. This continuously passivates the stainless steel band and places it in condition for continuous non-adhering plating and continuous clean stripping. Under conditions of manufacture where there is a probability that foreign particles might adhere to the surface of the base, it may be advantageous to employ a cathodic treatment in order to insure their removal. In any such case such treatment must be followed by an anodie treatment. such anodic electrolytic treatment, the foil will sometimes adhere to the depositing base, or isolated parts thereof. Such treatment additionally serves the purpose of cleaning the surface of the depositing base. Illustrative of such alkaline elec- Without trolytic baths are those composed of sodium hydroxide, sodium carbonate and sodium phosphate, although other alkaline preparations may also be used.

Following the mechanical cleaning and the anodic electrolytic treatment of the depositing base, I cause the latter to be immersed as the oathode in an electrochemical depositing bath of conventional type, after which the depositing base with the foil deposited thereon is immersed in a bath containing the reinforcing pull-off filmin a liquid condition, This film, although preferably an organic material, such as ethyl cellulose dissolved in a mixture comprising 20% ethylalcohol, 40% ethyl acetate and 40% toluol, need not necessarily be organic or thermoplastic but may be any suitable film-forming material having sufficient strength to act as a carrier for the foil and having properties such as solubility, which make it possible, if desired, thereafter to separate the film from the foil. For some commercial applications the foil, backed with the film, is entirely satisfactory, and in such cases it is unnecessary that the product be further treated. In many cases, however, particularly when the foil is to be used for embossing, the pull-ofi: film has too great strength to allow of clearcut embossing. I overcome this difficulty by entirely removing this film, after having attached to the opposite face of the foil a backing material such as waxed glassine 4 paper and readily separable therefrom during the embossing operation.

Referring to the drawings, an endless band [0, of the type heretofore disclosed, is mounted on mechanically actuated rollers H for continuous movement. The band is continuously advanced during the entire operation. A mechanical cleaner I2 is provided with rubbing apparatus, a preferred rubbing apparatus comprising rotatable or reciprocatory polishing heads l3. When the band has been thoroughly cleaned it is washed free of the mixture.

The cleaned and polished band is then washed again in a washer l5 and treated in an electrolytic bath IS, in which, as disclosed, the band is made the anode in order to obtain passivation. It is then passed through a washer l1, and through a conventional alkaline or other plating tank I8 wherein it is plated with an extremely thin layer of metal.

The plated band is now washed by passing through a washer I9, in which the washing is continued until the endless band and its plated layer are entirely free of any entrained plating bath fluid, and is then passed through a dryer 20. I have found that a suitable dryer for accomplishing the desired drying is of the hot air type in which the advancing band is continually met by counterfiowing hot air.

The dried plated layer is now coated with a film-forming material in a coating apparatus 2|. The coated layer and band are now passed through a second dryer 22, and the coat and the metal layer are mechanically separated in any conventional way from the endless band as indicated by the pull-off mechanism 23, thus producing a continuous metal foil 24 which may be wound in a rolled package 25.

The endless band continues to advance, and the operations are repeated, the polishing heads I3 now removing any particles of coating material which have penetrated through the pores of the metal layer to adhere to the polished surface of the metal band, during the preceding operation. The stainless steel band is thus continuously cleaned, polished, passivated, or anodically treated in an electrochemical bath, plated with a, metal layer, and coated, and the coated metal layer is continuously stripped from the steel band, whereby an endless length of metal foil is obtained although the stainless steel band is of relatively small and fixed length.

When the embossing foil is desired, it is necessary to remove the pull-off coating, which has too great a film strength to permit cleancut embossing, and substitute a backing having substantially-no film strength, and which is heat-releasable, a preferred material being a very thin size coating of shellac or varnish which is dried to such a physical form as to have no film strength. Before removing the pull-off coating a proper backing material, preferably waxed glassine paper, is attached to the face of the foil opposite to that having the to-be-removed pull-01f coating.

The strip, with its metal foil 24 and the pulloff coating 26, see Fig. 2, is therefore joined to a support 27, which, in the form I prefer, comprises glassine paper 28, having a wax face 29. A continuous strip of the waxed support is fed over a heated roller 33, and is pressed against the coated strip 26 by a gravity roller 31 or the like, the waxed surface 29 contacting the metal film 24. The waxed surface is softened and is momentarily melted as it contacts the metal film,

and then solidifies as the strips leave the rollers to form a combined strip 32, see Fig. 3, which has four layers, namely, the pull-ofi coating 26, the metal film 24, the Wax 29, and the glassine paper 28.

The pull-off coating is now removed by solvent action in a suitable solvent, a preferred method being to pass the combined strip over the surface of a tank containing solvent with the pulloff coating down. A suitable solvent for an organic backing such as ethyl cellulose is alcohol, and mechanical stirring of the solvent to hasten the solvent action may be provided if desired.

The resulting strip, see Fig. 4, consists of the metal foil 24, the wax 29, and the glassine paper 28, and is dried; it then receives a final varnish sizing 33 on the metal film surface to complete the embossing strip 34 as illustrated in Fig. 4. The varnish sizing may, if desired, be pigmented or dyed.

I claim:

1. A continuous process for the manufacture of extremely thin metal foils, comprising the steps of mechanically polishing an endless band of stainless steel, thereafter making the polished band the anode in an alkaline electrolytic bath to passivate the band and maintain it in condition for clean stripping, continuously electroplating a thin layer of metal on the surface of the treated band, applying a reinforcing pull-off film forming material in a solvent directly to the thin layer of electroplated metal, drying the film form ing material, and mechanically stripping the composite strip of thin metal and film from the endless band.

2. A continuous process for the manufacture of extremely thin gold foil, comprising the steps of mechanically polishing an endless band of stainless steel, thereafter making the polished band the anode in an alkaline electrolytic bath to passivate the band and maintain it in condition for clean stripping, continuously electroplating a thin layer of gold on the surface of the treated band, applying a reinforcing pull-off film forming material in a solvent directly to the thin layer of electroplated gold, drying the film forming material, and mechanically stripping the composite strip of thin gold and film from the endless band.

3. In the electrolyticproduction of thin metal foil by making an endless band of polished stain- 6 less steel the anode in an alkaline electrolytic bath to passivate the band and maintain it in condition for clean stripping, electroplating the metal on the surface of the treated band, applying a film forming material in a solvent directly to the electroplated metal, drying the film forming material, and subsequently mechanically stripping the composite strip of metal-and film from the endless band in foil form, the steps comprising preparing the stainless steel band by first brushing and then butting the same to obtain a surface having a mirror finish, anodically treating said surface in an alkaline electrolytic bath to passivate the band and maintain it in condition for clean stripping, and plating to a thickness of between about .000001 and .000015 of an inch on the treated surface.

CHARLES DAVIDOFF.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 676,357 E ndruweit June 11, 1901 1,287,793 Tillyer et al Dec. 17, 1918 1,425,184 Edison Aug. 8, 1922 1,731,415 Grupe Oct. 15, 1929 1,945,142 Fichtmueller Jan. 30, 1934 1,978,037 Yates Oct. 23, 1934 2,075,332 Antisell Mar. 30, 1937 2,133,685 Coughlin et a1 Oct. 18, 1938 2,282,350 Faust May 12, 1942 1,709,268 Hutchins Apr. 16, 1929 2,325,660 Chamberlain Aug. 3, 1943 1,096,822 Brandt May 19, 1914 2,133,685 Coughlin et al. Oct. 18, 1938 1,970,723 Wolfe Aug. 21, 1934 1,954,473 Dunn Apr. 10, 1934 1,978,151 Van Mater Oct. 23, 1934 2,327,870 Coxe Aug. 24, 1943 OTHER REFERENCES Schweizer Archiv fur Angewandte Wissenschaft und Technik, vol. 4, pages 289 through 293 (1938). Electrometallurgy, Supplement of the Metal Industry, pages 519-521, Nov. 22, 1935.

The Electrochemical Society Preprint 64-8, 1933, pages 83-97. 

